/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collector;
import java.util.stream.Collectors;

/**
 * A {@link BiMap} whose contents will never change, with many other important properties detailed
 * at {@link ImmutableCollection}.
 *
 * @author Jared Levy
 * @since 2.0
 */
@GwtCompatible(serializable = true, emulated = true)
public abstract class ImmutableBiMap<K, V> extends ImmutableBiMapFauxverideShim<K, V> implements BiMap<K, V> {

    /**
     * Returns a {@link Collector} that accumulates elements into an {@code ImmutableBiMap} whose
     * keys and values are the result of applying the provided mapping functions to the input
     * elements. Entries appear in the result {@code ImmutableBiMap} in encounter order.
     *
     * <p>
     * If the mapped keys or values contain duplicates (according to {@link Object#equals(Object)},
     * an {@code IllegalArgumentException} is thrown when the collection operation is performed.
     * (This differs from the {@code Collector} returned by
     * {@link Collectors#toMap(Function, Function)}, which throws an {@code IllegalStateException}.)
     *
     * @since 21.0
     */
    @Beta
    public static <T, K, V> Collector<T, ?, ImmutableBiMap<K, V>> toImmutableBiMap(
            Function<? super T, ? extends K> keyFunction, Function<? super T, ? extends V> valueFunction) {
        return CollectCollectors.toImmutableBiMap(keyFunction, valueFunction);
    }

    /**
     * Returns the empty bimap.
     */
    // Casting to any type is safe because the set will never hold any elements.
    @SuppressWarnings("unchecked")
    public static <K, V> ImmutableBiMap<K, V> of() {
        return (ImmutableBiMap<K, V>) RegularImmutableBiMap.EMPTY;
    }

    /**
     * Returns an immutable bimap containing a single entry.
     */
    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1) {
        return new SingletonImmutableBiMap<K, V>(k1, v1);
    }

    /**
     * Returns an immutable map containing the given entries, in order.
     *
     * @throws IllegalArgumentException if duplicate keys or values are added
     */
    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2) {
        return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2));
    }

    /**
     * Returns an immutable map containing the given entries, in order.
     *
     * @throws IllegalArgumentException if duplicate keys or values are added
     */
    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
        return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3));
    }

    /**
     * Returns an immutable map containing the given entries, in order.
     *
     * @throws IllegalArgumentException if duplicate keys or values are added
     */
    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
        return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4));
    }

    /**
     * Returns an immutable map containing the given entries, in order.
     *
     * @throws IllegalArgumentException if duplicate keys or values are added
     */
    public static <K, V> ImmutableBiMap<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
        return RegularImmutableBiMap.fromEntries(entryOf(k1, v1), entryOf(k2, v2), entryOf(k3, v3), entryOf(k4, v4),
                entryOf(k5, v5));
    }

    // looking for of() with > 5 entries? Use the builder instead.

    /**
     * Returns a new builder. The generated builder is equivalent to the builder created by the
     * {@link Builder} constructor.
     */
    public static <K, V> Builder<K, V> builder() {
        return new Builder<K, V>();
    }

    /**
     * A builder for creating immutable bimap instances, especially {@code public
     * static final} bimaps ("constant bimaps"). Example:
     * 
     * <pre>
     * {
     *     &#64;code
     *
     *     static final ImmutableBiMap<String, Integer> WORD_TO_INT =
     *             new ImmutableBiMap.Builder<String, Integer>().put("one", 1).put("two", 2).put("three", 3).build();
     * }
     * </pre>
     *
     * <p>
     * For <i>small</i> immutable bimaps, the {@code ImmutableBiMap.of()} methods are even more
     * convenient.
     *
     * <p>
     * Builder instances can be reused - it is safe to call {@link #build} multiple times to build
     * multiple bimaps in series. Each bimap is a superset of the bimaps created before it.
     *
     * @since 2.0
     */
    public static final class Builder<K, V> extends ImmutableMap.Builder<K, V> {

        /**
         * Creates a new builder. The returned builder is equivalent to the builder generated by
         * {@link ImmutableBiMap#builder}.
         */
        public Builder() {}

        Builder(int size) {
            super(size);
        }

        /**
         * Associates {@code key} with {@code value} in the built bimap. Duplicate keys or values
         * are not allowed, and will cause {@link #build} to fail.
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> put(K key, V value) {
            super.put(key, value);
            return this;
        }

        /**
         * Adds the given {@code entry} to the bimap. Duplicate keys or values are not allowed, and
         * will cause {@link #build} to fail.
         *
         * @since 19.0
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> put(Entry<? extends K, ? extends V> entry) {
            super.put(entry);
            return this;
        }

        /**
         * Associates all of the given map's keys and values in the built bimap. Duplicate keys or
         * values are not allowed, and will cause {@link #build} to fail.
         *
         * @throws NullPointerException if any key or value in {@code map} is null
         */
        @CanIgnoreReturnValue
        @Override
        public Builder<K, V> putAll(Map<? extends K, ? extends V> map) {
            super.putAll(map);
            return this;
        }

        /**
         * Adds all of the given entries to the built bimap. Duplicate keys or values are not
         * allowed, and will cause {@link #build} to fail.
         *
         * @throws NullPointerException if any key, value, or entry is null
         * @since 19.0
         */
        @CanIgnoreReturnValue
        @Beta
        @Override
        public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
            super.putAll(entries);
            return this;
        }

        /**
         * Configures this {@code Builder} to order entries by value according to the specified
         * comparator.
         *
         * <p>
         * The sort order is stable, that is, if two entries have values that compare as equivalent,
         * the entry that was inserted first will be first in the built map's iteration order.
         *
         * @throws IllegalStateException if this method was already called
         * @since 19.0
         */
        @CanIgnoreReturnValue
        @Beta
        @Override
        public Builder<K, V> orderEntriesByValue(Comparator<? super V> valueComparator) {
            super.orderEntriesByValue(valueComparator);
            return this;
        }

        @Override
        @CanIgnoreReturnValue
        Builder<K, V> combine(ImmutableMap.Builder<K, V> builder) {
            super.combine(builder);
            return this;
        }

        /**
         * Returns a newly-created immutable bimap.
         *
         * @throws IllegalArgumentException if duplicate keys or values were added
         */
        @Override
        public ImmutableBiMap<K, V> build() {
            switch (size) {
                case 0:
                    return of();
                case 1:
                    return of(entries[0].getKey(), entries[0].getValue());
                default:
                    /*
                     * If entries is full, then this implementation may end up using the entries
                     * array directly and writing over the entry objects with non-terminal entries,
                     * but this is safe; if this Builder is used further, it will grow the entries
                     * array (so it can't affect the original array), and future build() calls will
                     * always copy any entry objects that cannot be safely reused.
                     */
                    if (valueComparator != null) {
                        if (entriesUsed) {
                            entries = Arrays.copyOf(entries, size);
                        }
                        Arrays.sort(entries, 0, size,
                                Ordering.from(valueComparator).onResultOf(Maps.<V>valueFunction()));
                    }
                    entriesUsed = size == entries.length;
                    return RegularImmutableBiMap.fromEntryArray(size, entries);
            }
        }
    }

    /**
     * Returns an immutable bimap containing the same entries as {@code map}. If {@code map} somehow
     * contains entries with duplicate keys (for example, if it is a {@code SortedMap} whose
     * comparator is not <i>consistent with equals</i>), the results of this method are undefined.
     *
     * <p>
     * Despite the method name, this method attempts to avoid actually copying the data when it is
     * safe to do so. The exact circumstances under which a copy will or will not be performed are
     * undocumented and subject to change.
     *
     * @throws IllegalArgumentException if two keys have the same value
     * @throws NullPointerException if any key or value in {@code map} is null
     */
    public static <K, V> ImmutableBiMap<K, V> copyOf(Map<? extends K, ? extends V> map) {
        if (map instanceof ImmutableBiMap) {
            @SuppressWarnings("unchecked") // safe since map is not writable
            ImmutableBiMap<K, V> bimap = (ImmutableBiMap<K, V>) map;
            // TODO(lowasser): if we need to make a copy of a BiMap because the
            // forward map is a view, don't make a copy of the non-view delegate map
            if (!bimap.isPartialView()) {
                return bimap;
            }
        }
        return copyOf(map.entrySet());
    }

    /**
     * Returns an immutable bimap containing the given entries.
     *
     * @throws IllegalArgumentException if two keys have the same value or two values have the same
     *         key
     * @throws NullPointerException if any key, value, or entry is null
     * @since 19.0
     */
    @Beta
    public static <K, V> ImmutableBiMap<K, V> copyOf(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
        @SuppressWarnings("unchecked") // we'll only be using getKey and getValue, which are
                                       // covariant
        Entry<K, V>[] entryArray = (Entry<K, V>[]) Iterables.toArray(entries, EMPTY_ENTRY_ARRAY);
        switch (entryArray.length) {
            case 0:
                return of();
            case 1:
                Entry<K, V> entry = entryArray[0];
                return of(entry.getKey(), entry.getValue());
            default:
                /*
                 * The current implementation will end up using entryArray directly, though it will
                 * write over the (arbitrary, potentially mutable) Entry objects actually stored in
                 * entryArray.
                 */
                return RegularImmutableBiMap.fromEntries(entryArray);
        }
    }

    ImmutableBiMap() {}

    /**
     * {@inheritDoc}
     *
     * <p>
     * The inverse of an {@code ImmutableBiMap} is another {@code ImmutableBiMap}.
     */
    @Override
    public abstract ImmutableBiMap<V, K> inverse();

    /**
     * Returns an immutable set of the values in this map. The values are in the same order as the
     * parameters used to build this map.
     */
    @Override
    public ImmutableSet<V> values() {
        return inverse().keySet();
    }

    @Override
    final ImmutableSet<V> createValues() {
        throw new AssertionError("should never be called");
    }

    /**
     * Guaranteed to throw an exception and leave the bimap unmodified.
     *
     * @throws UnsupportedOperationException always
     * @deprecated Unsupported operation.
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    public V forcePut(K key, V value) {
        throw new UnsupportedOperationException();
    }

    /**
     * Serialized type for all ImmutableBiMap instances. It captures the logical contents and they
     * are reconstructed using public factory methods. This ensures that the implementation types
     * remain as implementation details.
     *
     * Since the bimap is immutable, ImmutableBiMap doesn't require special logic for keeping the
     * bimap and its inverse in sync during serialization, the way AbstractBiMap does.
     */
    private static class SerializedForm extends ImmutableMap.SerializedForm {
        SerializedForm(ImmutableBiMap<?, ?> bimap) {
            super(bimap);
        }

        @Override
        Object readResolve() {
            Builder<Object, Object> builder = new Builder<Object, Object>();
            return createMap(builder);
        }

        private static final long serialVersionUID = 0;
    }

    @Override
    Object writeReplace() {
        return new SerializedForm(this);
    }
}
